Protecting device for electric circuits



Sept. 4, 1951 1. 1 woRsHAM PROTECTING DEVICE FOR ELECTRIC CIRCUITS FiledJune 20, 1949 f I N VEN TOR. fry/z5?, Wffaz,

Waff/ey Patented Sept. 4, 1951 PROTECTING DEVICE FOR ELECTRIC CIRCUITSIrvin L. Worsham, North Little Rock, Ark., as-

signor of one-third to Roy L. Cochran, North Little Rock, and one-thirdto Azro L. Barber,

Lime Rock, Ark.

Application June 20, 1949, Serial No. 100,186 1 Claim. (Cl. 200-118)This invention relates to protecting devices for electric circuits andmore particularly to a device capable of forming a short-circuiting patharound a piece of apparatus which has been subjected to excessiveVoltage.

While concerned with electric circuits in general, the present inventionrelates more particularly to circuits for luminous tubes of the neontype which are supplied from a transformer which should be protectedfrom burning out in the event that the secondary becomes open circuitedby failure of apparatus in the secondary.

One of the principal objects of the invention is to provide a simple,cheap construction which is capable of functioning in either horizontal,upright or inclined positions and at the same time may be readilyreplaced with a minimum of trouble and expense.

Another object of the invention is to provide a protective device whichis normally non-conducting but when subjected to currents of apredetermined value becomes conducting so as to function in the natureof a protective relay.

Numerous other objects and advantages of the invention will appear fromthe following description when it is read in connection with thedrawings in which:

Figure 1 is a diagrammatic view of an application of the presentinvention to a luminous tube display sign;

Figure 2 is a longitudinal sectional View of the protective deviceembodying the present invention;

Figure 3 is a section similar to Fig. 2 showing a modified construction;and

Figure 4 is a longitudinal section of a unitary construction in whichthe protective device is mounted co-axially with a luminous tube to beprotected.

Referring first to Figure 2 of the drawing, reference character 5designates an insulating tube preferably of glass sealed in at its endsby metal y caps 6 and 1. These caps may be constructed to be held inspring clips like an ordinary cartridge fuse or may be provided withwire connections, as indicated in the drawings. Mounted within the tubeand contacting the two end caps 6 and 1 respectively are two resilientconducting springs 8 and 9 preferably made of material such as springbrass. Interposed between the free ends of these springs is aninsulating member or capsule l0 which may be composed of gelatin or someother material which is an insulating material under normal conditionsbut which will carbonize and electrically connect ends of springs 8 and9 when the circuit to be protected carries excessive current. As shown,the free ends of the springs are reduced in cross section so as toinsure good contact with the member or capsule l0.

Figure 3 shows a modied form of protective device in which a singleconducting spring Il is mounted within the tube 5 and engages thecapsule l0. One of the sealing discs designated I3 for the end of tube 5forms a terminal, whereas the terminal adjacent the capsule illcomprises a disc I2 to which the conducting wire is connected. The discl2 engages the scaling disc l2a, as indicated.

Figure 1 shows one practical application of the invention to a neon signsupplied with current from the transformer T, primary l-6 of which isconnected to any suitable source and having a secondary l5 whichsupplies current to the neon tube designated generally by referencecharacter I4. The part I4 may be of any conventional form which usuallyconsists of a glass tube filled with gas which becomes luminous whencurrent is applied to it. The sections of tube are connected by means ofsealing joints ,-ll and, for purposes of adequate protection, differentsections of the tubes are shunted by protective devices a., b and cwhich may correspond to the embodiments of the invention shown in eitherFigure 2 or Figure 3.

Whenever conditions arise, for instance in the portion of the signshowing the letters Go so as to apply voltage to the protective device ain excess of that to which the device is capable of withstanding, thegelatin capsule l carbonizes, forming a conducting path between the endsof springs 8 and 9 and thus short circuiting the section of the sign towhich it is connected. Under these conditions, the secondary I5 willremain close circuited so as to supply the remainder of the luminoustubes so that the device a is in series with the letters od and Eats.yThe glass-tube 5 may carry a paper label which will become charred whenthe capsule carbonizes so as to give an exterior indication of thefailure. The device a. may then be replaced to restore operation of thecircuit. Were it not for the protective device forming a currentcarrying means around a portion of the sign, a failure of one part ofthe sign would cause a failure of all of the sign and possibly a burningout of the transformer. The protective device of this invention simplyand effectively overcomes that possibility with a minimum of expense.

In the figures so far described, no attempt has been made to show theactual manner of securing the protective device in circuit with theelectric sign and it is to be understood that while a spring clipattaching means will be useful, any other suitable form of constructionmay be adopted.A ,o ,c Y

Fig. 4 of the drawing shows a construction or arrangement in which theprotector 25 is in series with a short piece of luminous or gaseoustubeor resistance equivalent to the same whichse'rves to absorb thepotential buildup in the secondary winding of the high tensiontransformen fIhe terminals or lead wires 2B are connected in parallelwith a sign or lthe lighting proper.. In the event any tube connected tosecondary I9 breaks or secondary circuit otherwiseopens high Voltagecurrent follows the path of 1e`a`st'1sis't'anc`e which would be through20 arcing over protector disintegrating capsule IU in Fig. 2, creatingconduc` tive carbon suiiicient to feed tube 2 |or equivalent resistancewithfsufcient current to Villuminate same; this alleviates the. stressin the secondary of the transformer which 'is ofa current limit type. Tosummarize, luminous tube'2 l A-is in series With protector 25. This4arrangement is 'to be eon= nected in parallel with the secondaryterminals leading tolum'inous tubesor to a-neon sign. Tube 2i lights upwhen the `"proi'ft-ic-tor 25 is spent, thus relieving the secondar" 'ofpotential buildup and it stays lighted until repairs are r'na'de and theprotector is replaced.

The `devicefrn'ay :embody the strlucture of either Fig. 2 or Fig. 35ansit wiii beso designed that lupon the occu rence f excessive current flowthrough the tube `2'l j`t le "ID Willcarboniz'e while completing 'adirecte 'cuit between the two spring wires B arid 9 '5i eiwe spring wireii and conducting plate J 2 th'us enabling the tube "departing fromltrie spirit and ing the possibility of transformer burnout or dangerousfire hazards.

`One of the outstanding advantages of the present construction is itsability to function in either a horizontal or `a vertical position.Brotective de vices of this lgenera-1 truite, as proposed heretofore,have been effective only when placed in a horizontal position so thatthe fusing material actually flows and connects the two end terminalsupon rsolid-iiicaticn. The present invention makes any such precisepositioning unnecessary and yet simpliiies the construction to a markeddegree.

While Ihave Adescribed only a few forms of my -inventiom it is to beunderstood that changes and-rnodic'atio'ns may be made in the detailswithin thescopeof the appended claim without scope of my invention.

Having thus described my invention, I claim: A cutout for luminous tubecircuits comprising *etal terminal at each ncl of 1ro 4coil springs lof`con iuctive niaterial exten iig gt'hwi'seof the tube, neend of each ofsaid Springs ritacting 'one of said terminals, and a gelatinous`capsifile eirtndlhg lengthwise `of the tube disposed vbetwe"eri the.other ends 5f. Sie eens-s, sammle up@ overvolta'ge 'on fthe:l beingadapted to ncarbenize to forni an electricunductor n.

IRVIN L. WORSHAM.

animatrices CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name v wD`ate,

i 628,115 rettet T Juiy 4, 1899 2,179,935 igifatt v Nov. 1 4, 119392,463,745 'Coiardo Mar. is, 1949

